Definition and Characteristics
Ashphalt is a bituminous material meaning it is a sticky, highly viscous liquid. Most natural bituimens contain sulfur and heavy materials such is nickel, lead, mercury or arsenic. It is commonly confused with tar. Tar is a by-product of asphalt, and used on many flat roofs.
The natural Asphalt is created from ancient microscopic algae deposited in the mud on the bottom of the ocean and compressed under pressure.
Man-made asphalt comes from separation of oils such as gasoline and diesel. Special machines and processes are used for the separation, and then the asphalt is "blown," meaning oxygen is added making it stronger and more viscous. 
Use in Buildings
Historically, asphalt was used as brick mortar and for waterproofing. In the 1830s, France was the first to make asphalt popular for pavements and roofs.
Today, the most common use of asphalt in buildings is asphalt roof shingles. Shingles sometimes are made from wood and paper, but that has become less popular due to fire issues. Each shingle overlaps with the next and the top of the roof is folded around the peak to best prevent water seepage. Asphalt shingles are available in many different colors, shapes and sizes.
Benefits and Drawbacks
Asphalt shingles are better than wood shingles because they are fire proof and less prone to rotting. They are also lighter than clay tiles, which is a benefit considering earthquake risks. Asphalt shingles are easy to maintain and install.
Since asphalt shingles are oil based, and over time the sun will dehydrate these oils, causing the shingles to shrink, and potentially seeping to the building materials below. It is now common practice to have a secondary water proof member under the shingles to prevent any water seepage from meeting wood structures and causing rot.
Rain water is also capable of eroding the shingle surface. 
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